1. Field of the Invention
The present invention relates generally to a method for making a fruit-containing yogurt product and, more specifically, to a method for making a low fat, low calorie fruit-containing yogurt product having the appearance, texture and taste of conventional thin-bodied fruit-containing yogurt.
2. Description of the Prior Art
Yogurt is, conventionally, a cultured milk product produced by fermenting sources of butterfat, such as milk, skim milk, cream, nonfat milk solids, and the like, in liquid or powder form, with a yogurt culture producing lactic acid. Depending upon the butterfat source employed, other ingredients and the processing treatment, yogurt may be prepared in various forms. Frozen yogurt, at one extreme, is generally consumed in hard frozen or soft serve form. Liquid yogurt, at the other extreme, is consumed by drinking as contrasted with by use of a spoon. The most common or so-called conventional form of yogurt is firm bodied, smooth and viscous, generally having the consistency of a light gel which is pudding or custard-like and spoonable. What has now become known as European style yogurt is a thin-bidied version of conventional yogurt, having a viscosity of 2 to 10 cm, preferably 4 to 8 cm, but not as thin as liquid yogurt, and not drinkable. Fruit-filled yogurts are made Sundae style with fruit on the bottom, Swiss style with the fruit pre-mixed, or Western style with the fruit on the bottom and the yogurt colored and/or flavored. Most plain yogurt (unfruited) on the market contains from 120 to 150 calories per 8 ounce (227 grams) serving. Most fruited yogurts contain 240 to 270 calories per 8 ounce (227 gram) serving. Milk product bases for yogurt, depending on taste, display varying butterfat contents and yogurts may be prepared with fat contents varying from as low as less than 0.4 percent by weight up to about 20 percent. According to FDA labeling standards, yougurt may be labeled as "nonfat" if it contains 0.4% or less butterfat; as "lowfat" if it contains from 0.5% to 2% butterfat; and as fullfat or regular yogurt if it contains at least 3.25% butterfat. Most commercially available yogurts are "lowfat" by FDA labeling standards.
In recent years yogurt has enjoyed immense popularity. The beneficial effects on health due to the therapeutic properties of the bacterial cultures contained in yogurt are well known. In addition, yogurt has become a popular food among dieters. To increase its appeal, the sharp, tangy taste characteristic of plain, unflavored yogurt, which heretofore made yogurt unacceptable to many people, has been masked in many yogurt products with fruit and sweeteners. This practice has resulted in a flavored yogurt product that is more palatable to a wider segment of the population. However, the use of these additives has been accompanied by an increase in product calorie content from the about 120 to 150 calories per eight ounce (227 grams) serving of plain, unflavored yogurt to about 240 to 270 calories per eight ounce (227 grams) serving of the sweetened, fruit-containing yogurt. Such a high calorie content renders the fruited product generally unsuitable for inclusion in reducing diets since the fruit yogurt uses up the majority of the calories usually alloted to a single meal. As a result the dieter has difficulty choosing a sufficient variety or quantity of foods to form a balanced meal within the remaining calories allowed. Accordingly there has existed for some time a need for a fruit-containing yogurt product which is low in calories, fat and carbohydrate content.
There have been efforts, none of them totally successful, at producing a sweetened or flavored yogurt product with a relatively low butterfat content but which exhibits the characteristic creamy consistency and desirable flavor, appearance and mouth feel of conventional full-bodied custard or pudding-type yogurt products while, at the same time, overcoming the high calorie and high carbohydrate problems accompanying the use of fruited or flavored yogurt. One very important reason for the apparent inability to achieve this goal is that yogurt made from really low fat milk products, e.g., less than about 0.5% butterfat, is typically loose and watery and lacking in flavor, rather than creamy and with consumer acceptable flavor, appearance, body and mouth feel. Moreover, yogurt having such an undesirably thin consistency does not blend well with fruit additions and, therefore, the fruit additions do not meaningfully add to the attractiveness and palatability of the yogurt product. Efforts to overcome this problem to obtain a palatable product have either required adding flavor influencing milk solids, which increases the yogurt calorie and carbohydrate contents, or increasing the butterfat content, which has a similar effect. It will, therefore, be appreciated that in the production of fruited yogurt, acceptable solutions to taste and diet problems appear to adversely affect appearance, body and mouth feel characteristics, and vice-versa. Accordingly, it is not at all surprising that, to date, no fully acceptable low fat, low calorie, fruited yogurt product has become available.
The problems associated with preparing a consumer acceptable low fat, low calorie, fruited yogurt become even more difficult when the yogurt product sought to be produced is the so-called European style yogurt. Due to localized destabilization of the yogurt, thin-bodied yogurt products tend to whey off more readily, resulting in separation of the moisture and the curd. Free whey or moisture accumulates around the edges of the yogurt cup and covers all or part of the product surface. The result is an unattractive product which is unappealing to consumers. In the context of a thin-bodied, low fat yogurt product, where the use of relatively large amounts of stabilizers to absorb water and prevent whey leakage is not a viable approach due to the undesirable thickening or body-creating effect of such stabilizers and where the emulsifying capacity of butterfat is effectively non-existent, wheying off is a difficult problem to deal with.
To be sure there have been serious efforts at producing fruited yogurt products having at least some of the foregoing desirable attributes--i.e., low fat, low calorie, thin-bodied, and consumer acceptable appearance, body, texture and mouth feel. For example, in U.S. Pat. No. 3,969,354, Pavey et al teach the production of a fruited, flavored yogurt which has a relatively low, not exceeding about 0.5% by weight, butterfat content. However, the Pavey method requires post-culturing heat treatment and homogenization to achieve whey separation, extensive curd coagulation, and product restructuring. As a result, the appearance, body and mouth feel of the Pavey yogurt will be demonstrably distinguishable from a product not so treated. Moreover, the Pavey process does not purport to produce a thin-bodied product and makes no effort to control or minimize the calorie content of its resulting yogurt product in order to produce a product which is below the 240 to 270 calories/8 ounce serving calorie content of conventional fruited yogurt products. In U.S. Pat. No. 3,128,190, Donay discloses the use of a skim milk starting material. However, the process for making Donay's fruit-containing yogurt requires fruit which is precooked with sucrose to prevent fermentation thereof by the yogurt cultures with resultant unpleasant flavors. As a result of this procedure the Donay et al method neither produces really low fat yogurt nor reduces the high calorie and carbohydrate content of conventional fruit-containing yogurts. Moreover, the Donay product has a semi-solid consistency similar to ice cream and quite clearly does not prepare a thin-bodied yogurt product. In U.S. Pat. No. 4,110,476, Rhodes discloses a process for preparing liquid or frozen, rather than thin-bodied custard-type, yogurt products which utilize whey protein concentrate together with milk products as the starting material ingredients and contain higher sugar contents than are desirable for a fruit-containing yogurt product suitable for a reducing diet. According to Rhodes, the whey protein concentrate allows the preparation of a liquid or frozen yogurt by preventing wheying off, curd formation and casein precipitation. In U.S. Pat. No. 3,269,842, the fruited yogurt product produced by the Mayer et al process has a fat content of about 4% and appears to be an undesirably high calorie, high carbohydrate product.
Probably the most ambitious effort at producing a consumer acceptable low fat, low calorie, low carbohydrate yogurt product is disclosed in U.S. Pat. No. 4,410,549--Baker wherein a low calorie, low fat, fruit-containing yogurt is prepared by a process including the steps of admixing skim milk, stabilizers and heat modified nonfat dry milk solids, and processing the mixture by heating, homogenizing, fermenting with a culture mixture of Lactobacillus acidophilus, Lactobacillus bulgaricus and Streptococcus thermophilus, blending with low calorie fruit preserves and cooling. The heat modified nonfat dry milk solids are derived from a process in which condensed skim milk is subjected to non-coagulative direct steam heating prior to spray drying. Notwithstanding that the resultant yogurt product had the consistency, texture and taste of conventional firm-bodied custard or pudding type, and not of thin-bodied, fruit-containing yogurt, the packaged product nevertheless exhibited puddling, i.e., it released free moisture which accumulated around the edge of the yogurt cup and covered all or part of the product surface. This departure from the conventional and consumer-anticipated appearance of yogurt is an undesirable aspect of the product of the Baker process.
It is, therefore, apparent that despite the numerous efforts to produce a satisfactory, low fat consumer acceptable yogurt product, there still exists a need for such a product and, in particular, for a low fat, fruit-containing yogurt which is low in calories while resembling conventional thin-bodied yogurt in appearance, texture, body and taste.